This invention involves a method for producing high purity germane by a continuous or semi-continuous process. The typical preferred commercial method for producing germane is an aqueous borohydride reduction of germanium dioxide, most often using sodium borohydride or potassium borohydride. Examples of this process may be found in U.S. Pat. No. 4,668,502 of Russotti; U.S. Pat. No. 7,087,102 of Withers et al.; and U.S. Patent Application Publication No. 2008/0299037 of Tezock.
Russotti, Withers et al. and Tezock are all directed to the yield and purification of germane from germanium dioxide. In particular, Withers et al. disclose a method for purifying a germane fluid, produced by a cryogenic-trapping technique. However, the co-product of the reduction, namely hydrogen gas, is not considered or discussed in detail in Russotti, Withers et al. or Tezock.
In general, in such reductions, impure germane leaves the primary process reactor entrained in a hydrogen gas stream at a volume concentration of approximately 2% to 20%. The presence of the co-product hydrogen gas presents enormous difficulties for high volume production of germane, particularly if the purification is completed in a batch-wise low temperature condensation of the germane out of the hydrogen stream. An article by W. Jolly published in the Journal of the American Chemical Society discusses the formation of hydrogen and removal of the germane from the hydrogen gas stream by cryogenic trapping (W. Jolly, J Am. Chem. Soc., V. 83, p. 335 (1961)).
While methods for removal of the hydrogen gas, such as membrane separation and absorption, are alternatives which may potentially allow for continuous purification of the germane, such methods have not to date been reduced to practice. Accordingly, a method for producing high purity germane on a semi-continuous basis without the need for low temperature process conditions, such as those required for cryogenic trapping processes, would be desirable.